title: Flexible C2-symmetric bis-sulfoxides as ligands in enantioselective 1,4-addition of boronic acids to electron-deficient alkenes.
abstract: The application of acyclic C2-symmetric chelating bis-sulfoxide ligands in the Rh(I)-catalyzed enantioselective 1,4-addition of boronic acids to electron-deficient alkenes is reported. Among the acyclic ethane-bridged bis-sulfoxides tested, the ligand Ferbisox (11), bearing ferrocenyl moieties as substituents at the sulfinyl sulfurs, has exhibited the best results in terms of chemical yield (up to 96%) and enantioselectivity (up to 97% ee). The conjugate addition takes place smoothly in toluene at room temperature in short reaction times (typically 2 h). The reaction scope, including the use of different boronic acids, five-, six-, and seven-membered cyclic enones, an unsaturated lactone, and the most challenging acyclic ketones, is reported. An X-ray diffraction study of the [Ferbisox·RhCl]2 precatalyst clearly exhibits a dimeric structure with an S coordination of the sulfoxide to rhodium. On the basis of the X-ray data and on structural studies conducted in solution by (1)H NMR, a model explaining the high enantioselection observed is proposed.
authors.affiliation: Instituto de Investigaciones Quı́micas, CSIC-Universidad de Sevilla, c/. Américo Vespucio, 49., Isla de la Cartuja, 41092 Sevilla, Spain. khiar@iiq.csic.es
authors.forename: Noureddine
authors.initials: N
authors.lastname: Khiar
authors.forename: Álvaro
authors.initials: Á
authors.lastname: Salvador
authors.forename: Victoria
authors.initials: V
authors.lastname: Valdivia
authors.forename: Ahmed
authors.initials: A
authors.lastname: Chelouan
authors.forename: Ana
authors.initials: A
authors.lastname: Alcudia
authors.forename: Eleuterio
authors.initials: E
authors.lastname: Álvarez
authors.forename: Inmaculada
authors.initials: I
authors.lastname: Fernández
mesh_terms: D000475:Alkenes / Q000737:chemistry*; D001897:Boronic Acids / Q000737:chemistry*; D004583:Electrons; D008024:Ligands; D008958:Models, Molecular; D008968:Molecular Conformation; D013237:Stereoisomerism; D013454:Sulfoxides / Q000138:chemical synthesis / Q000737:chemistry*
chemical_list: D000475:Alkenes; D001897:Boronic Acids; D008024:Ligands; D013454:Sulfoxides